Long Term Evolution Advanced (LTE-A) is a wireless communication standard developed by 3rd Generation Partnership Project (3GPP). Recently, low cost machine type communication (MTC) UEs has been under discussions in 3GPP meetings to consider various potential deployment scenarios for the LTE-A wireless communication systems. As the trend of future wireless technology may gravitate toward pervasive wireless nodes such as smart meters, household appliances in work networks, smart health caring devices, smart security devices, and so forth, ways to extend current technology to accommodate MTC devices have been under discussions.
Future MTC devices could be regarded to be low cost, small, and pervasive. Some of them may even possibly be located in deep indoor environment such as in a basement that could be many floors deep. The transmission and reception abilities of such MTC devices could be assumed to be quite limited as having limited bandwidth usage, limited buffer, limited antennas, and so forth. In order for such MTC UE to attach to a base station, the MTC UE would need to first initiate a cell search procedure in order to attach to the cell of the base station. However, the cell search procedure could potentially be challenging for a difficult to reach MTC UE, and the challenge is to be explained in further details.
FIG. 1 serves to illustrate a typical cell search procedure for a wireless communication system. During a cell search procedure, assuming that a MTC UE 102 has awoken from a dormant state and seeks to attach to a closest base station, such as base station 101. In step S101, The UE 102 would be required to read a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) in order to obtain essential information such as information related to a cell identification (ID) of the base station 101 or frame timing information. The cell ID could be the physical cell identifier (PCI) in the case of LTE. As the result of obtaining the PCI, in step S102, the UE 102 would be able to read a cell specific reference signal (CS-RS) to complete the synchronization procedure. After the synchronization procedure, in step S103, the UE 102 would read from a broadcast channel such as a physical broadcast channel (PBCH) for the master information block (MIB), or in step S104, the UE 102 would be able to read from the physical downlink shared channel (PDSCH) for the system information block (SIB).
Information in the PBCH would then undergo a channel coding and modulation process. In particular, 40 bits of MIB may pass through a channel coding process, a rate matching process, and a scrambling process. After the scrambling process, the data would be modulated using QPSK. Subsequently, the rest of processes would involve layer mapping, precoding, resource mapping, and OFDM generation. For the case of LTE, The detailed descriptions of these processes are described in section 6.6 of “Physical Channels and Modulation,” 3GPP TS 36.211, V11.2.0, 2013-02 which is incorporated by reference and also section 5.3 of Multiplexing and channel coding,” 3GPP TS 36.212, V11.2.0, 2013-02 which is also incorporated by reference.
FIG. 2 illustrates the resource location of a PBCH according to a current standard of the LTE communication system. Typically, system information in the MIB would require at most 4 radio frames 201 or 40 transmission time intervals. In other words, the system information in MIB of a cell would not change for at least 4 radio frames. Each radio frame 203 contains 10 subframes with each subframe 206 having two slots, namely slot 0 and slot 1. The radio resource of a PBCH 202 according to FIG. 2 is allocated in slot 1 of the 0th subframe, and a PBCH 202 is allocated in the central 6 physical resource blocks of transmission frequency band and the first four Orthogonal Frequency Domain Modulation (OFDM) symbols 207 of slot 1 of a subframe 206.
However, if a MTC UE is located in difficult to reach places and is thus unable to discern information from the PBCH broadcasted from a cell, the UE would not able to attach to the cell. Therefore, in order to reach MTC UEs in hard to reach places such as underground without incurring extra costs by inserting additional technologies, existing communication infrastructures may need to improve their coverage by an additional 15˜20 decibel (dB) in order to enhance coverage for MTC devices. In order to extend the PBCH coverage, one idea could be to increase repetition of the number of MIB transmissions. FIG. 3 illustrates a crude example of such concept by repeating PBCH transmission multiple times within each radio frame. By repeating an identical PBCH transmission multiple times, the broadcast coverage of a cell could be extended at the expense of a larger amount of system capacity. Therefore, this solution would not be optimal.